The purpose of this application is to conduct an evaluation of synchrotron X-ray beams in K-edge digital subtraction angiography (DSA) with emphasis on the coronary arteries. The intense and tunable synchrotron radiation produced at electron storage rings provides a new source of X-rays highly-suited to iodine K-edge DSA. The high intensity and small angular divergence permit the radiation to be monochromatized by Bragg diffraction and made available in beams of small vertical size, of arbitrary horizontal width, and of tunable energy. The use of such beams provides maximum sensitivity to intra-arterial iodine and virtually eliminates image contrast due to non-vascular body structures. The intensity of the beams permits short exposure times and allows images to be recorded, in line-scan fashion, in sharp focus despite arterial motions. The sensitivity of this method to iodine offers the prospect of visualizing arteries by peripheral venous injection, and in particular the coronary arteries. Preliminary studies by the authors have already demonstrated the principles of K-edge DSA using phantoms and excised animal hearts with an existing tunable X-ray beam at the Stanford Synchrotron Radiation Laboratory (SSRL), and in vivo studies with animals has begun. For this application an existing beam at SSRL will be widened to accommodate human subjects, a patient examination room with the proper medical equipment will be assembled, and an evaluation conducted, first with animal and then with human subjects, by a comparison of non-invasive (DSA) and invasive (standard) angiographic procedures. It is expected that the same instrumentation will be operated subsequently in a tunable X-ray beam at SSRL exclusively for research and clinical studies.